For detecting oxygen concentration in an exhaust gas from an internal combustion engine, in order to exhibit a detecting function, an oxygen sensor is employed composed of a sensor element formed with an exothermic element for heating an oxygen concentration detecting portion being integrally laminated with the detecting portion.
Such an oxygen sensor is disclosed in, for example, the Japanese examined Patent Publication No. 36461-1988 or the Japanese Laid-open Patent Application No. 222159-1987.
As shown in FIG. 11, the former publication discloses electrodes 105 and 107 which are laminated on both faces of a solid electrolyte layer 106, which are laminated on an insulating body 101 having a gas penetrating property to form an oxygen concentration detecting portion, on which is laminated an exothermic element 103 to form a sensor element 1 of a thin plate configuration. On the other hand, as shown in FIG. 12, the latter application discloses a side face of a cylinder-shaped insulating material 110 having an air introducing hole 110a provided and a through hole 110b communicates with the air introducing hole 110a. An oxygen concentration detecting layer in which electrodes 105 and 107 are laminated on both faces of a solid electrolyte layer 106, is laminated on an exothermic element 103. Element 103 is then laminated on the insulating material 110 covering the through hole 110b to form a hollow and cylinder-shaped sensor element 1.
However, in the Japanese Patent Publication No. 36461-1988 the sensor element has a thin plate configuration, causing problems since it is weak from a view of strength to easily suffer breakage and damage due to vibration and shocks. On the other hand, Japanese Patent Application Laid-open No. 222159-1987 has a large heat capacity on account of the hollow and cylinder-shaped sensor element which has a low heating efficiency of the sensor element by the exothermic element, so that there is a problem, since it cannot exhibit its function immediately during the start-up of an internal combustion engine and the like in which rapid heating of the sensor element is required.
The present invention has taken the above circumstances into consideration, the object of which is to provide an oxygen sensor which is composed of a sensor element being strong against vibration and shocks and capable of performing rapid heating.